How to fault-find an electric shower

Helpful video reference. DNA Power Solutions is a UK electrician based in Corby. This video follows an actual electric shower fault from initial call-out through to the repair — a useful demonstration of the systematic approach and what each internal component looks like when it has failed. Worth watching before you remove the shower casing for the first time.

1. Understand the common failure points

Electric showers are simpler inside than they look. The components that most commonly fail are:

• The heating element — a resistive coil that heats the water as it passes over it. Limescale in hard-water areas is the most common cause of failure, either from gradual build-up or from a sudden open-circuit break.
• The thermal cut-out (TCO) — a safety device that trips if the element overheats. On some showers it can be reset by hand; on others it is a one-shot device that must be replaced.
• The solenoid valve — an electromagnetic valve that opens to allow water flow when the shower is switched on. The coil can fail, or the valve can seize open or closed.
• The pressure switch — confirms water is flowing at adequate pressure before energising the element. A failed switch can prevent heating even when flow looks normal.
• The MCB or RCBO — a short circuit or failing element can trip this, or the breaker itself can fail mechanically over time.

2. Test the supply at the shower unit

Before removing any cover, check whether the fault is in the supply or inside the unit. With appropriate care, test for 230 V at the shower's terminal block with the isolator switched on.

If you read 230 V and the shower is still dead, the fault is internal — proceed to the element and TCO tests. If you read 0 V with the isolator on, the fault is upstream: MCB, isolator or the circuit cable.

A partial reading — voltage present but low, or fluctuating — suggests a loose connection at the terminal block or a neutral fault. Re-terminate any loose conductors before going further.

3. Check the MCB or RCBO at the consumer unit

Go to the consumer unit. If the shower's breaker is tripped, reset it and observe. An MCB that trips again immediately suggests a short circuit — inside the shower unit or in the circuit cable itself. An RCBO that trips suggests an earth fault, often from damaged insulation or a failing element leaking current to earth.

If the breaker resets and holds but the shower still does not work, the fault is inside the unit — usually the element or TCO.

A breaker that feels loose, will not stay in the on position, or shows signs of heat damage should be replaced even if the shower is the primary fault. A weak breaker cannot protect the circuit reliably if the fault recurs.

4. Test the heating element

Isolate the circuit and confirm dead. Locate the element terminals inside the shower casing and disconnect the element leads. Measure the resistance across the element terminals with a multimeter set to ohms.

Calculate the expected value using: R = V² ÷ W. For a 9.5 kW shower at 230 V: R = 230² ÷ 9500 = 5.57 Ω. A reading within 10% of this is healthy. An open circuit (OL on the display) means the element has burned through and needs replacement. A reading of zero suggests a short — less common, but also means replacement.

In hard-water areas, elements typically last four to seven years. In soft-water areas, considerably longer.

5. Test the solenoid valve

The solenoid valve sits on the water inlet inside the shower unit. Disconnect the two wires to the solenoid coil and measure their resistance. Most shower solenoids read between 300 Ω and 600 Ω. An open circuit means the coil has failed.

A solenoid coil can test fine electrically and still fail mechanically — limescale on the plunger can prevent it moving even when the coil is energised. If you have confirmed the supply is live, the coil reads correctly, and the shower still produces no water flow, the valve plunger is likely seized and the valve needs replacement.

6. Test the thermal cut-out

The TCO is usually a small disc or cylinder attached directly to the element or its housing. Set your multimeter to continuity or low ohms and test across its two terminals.

A healthy TCO reads close to zero ohms. A tripped TCO reads open circuit. Check the shower manufacturer's instructions to confirm whether the TCO on your model can be reset — many have a small reset pin accessible through a hole in the body. Once reset, test for continuity again before energising.

If the TCO has tripped repeatedly, the underlying cause is overheating — usually a failing element or restricted water flow — and replacing the TCO alone without addressing the root cause will result in another trip shortly after.

7. Test the pressure switch

The pressure switch is a small component in the water flow path, typically with two or three terminals. In most showers, it closes when water pressure is detected. Test continuity across the switch terminals with the water supply turned on and the shower switched to its run position (with the shower circuit isolated at the unit rather than at the board).

If you have confirmed the element, TCO and supply are all healthy but the element still does not energise, and the switch remains open when water is flowing, the pressure switch has failed and needs replacing.

8. Replace the faulty component or call an electrician

Replacement elements, TCOs and solenoid valves for most mainstream UK shower brands — Triton, Mira, Aqualisa, Bristan, Redring — are available online, often for under £30. Replacing internal components inside a shower unit is maintenance work and does not require Part P notification.

If the fault is in the circuit wiring — a damaged cable, a failed RCBO, or a loose connection at the consumer unit — that work is notifiable under Part P and should be carried out by a qualified electrician. Similarly, if you have worked through these tests and cannot find the fault, call an electrician rather than continuing to probe around an unfamiliar installation.

When to call us

Shower fault-finding in Sandwich is the kind of small job Richard takes on at the £10 per 10-minute rate. If the fault turns out to be in the circuit rather than the shower unit — a failed RCBO, a damaged cable, or anything that needs certifying — he can deal with that on the same visit.